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I've got a 2003 Silverado 5.3 4x4. like the title says I'm getting p0300 random misfire when it rains, I can drive for about 20 min at highway speeds before it starts misfiring. The torque converter will unlock an it studders an loses power. I've been throwing parts at this thing for about 4 months, plugs,wires,coils,fuel pump(the pump went bad while driving home from work) I've unplugged every connector in an around the engine bay clean an put dialectic grease in them.I was getting a lean bank 1 code an found bad intake gasket (used the water bottle trick) I replaced the intake gaskets an I thought that fixed my issue. I was coming home from work last night in the rain an about 20 min into my drive the issue came back. Sometimes it can set for 3 or 4 days an the code will go away an be fine, somtimes it'll take a month. I have a cheap luanch scan tool that does live data but I'm not sure where to go to from here or what to look at next. Cylinders 2 an 7 are missing firing the worst with 7 misfiring more than 2.the only codes I'm getting is the p0300 an p0449 (evap code that's been on since I got the truck) any help or pointers would be great thanks
If I can remember my Chevy engines cylinder 7 comes right before 2 in the firing order which may or more likely no be of any significance as it is a coil pack engine.
Normally a misfire in damp weather points straight to an insulation failure on the secondary (high voltage) side of the ignition but the 20 minutes driving time points more towards a heat related issue such as crank or cam sensor.
Anybody seen this before ?
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I would think if it was heat issue it would happen all the time not just in the rain ? ...at this point I'm open to try about anything though lol. Thanks for the reply
#7 plug wire isn't chaffing or touching the exhaust? Missing the inner fender cover on the odd bank side?
I'd mist the ignition components around #7 and hover a test light over them connected to ground to look for arcing, inspect the plug for signs of tracking and probably give the plug wires a goodly gob of dielectric grease.
Thanks for the reply Noah, no rubbing on the wires an has both inner fender covers. I've put dia-electic grease on all the wires an sprayed everything a couple times. I cant seem to recreate the problem for nothing when it's running good. But I was checking the connection on the fuel pump today an found the filler neck was bad, maybe getting water in the gas? My local parts store didnt have one in stock so I ordered one. I'm gonna drain the gas that's in it (only 1/8 of tank) an put fresh gas in I'll let ya guys know if that helps any
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